Unstable Telescopic Resonator Research Articles

Analytic model for unstable telescopic resonator with an active medium to a two-dimensional geometrical approximation

The design of an unstable telescopic resonator with an arbitrary configuration of the active medium inside the resonator was evaluated for cases of outcoupling of radiation from a concave mirror or from a convex mirror. The calculation makes it possible to assess routinely the energy parameters of laser systems without using high-performance computers.

Properties of radiation emitted by an oxygen—iodine chemical laser with an unstable telescopic resonator and an exit mirror with a Gaussian reflectivity profile

A numerical study is reported of the spatial distribution of the radiation emitted by an oxygen—iodine chemical laser with an unstable telescopic resonator and an exit mirror with a Gaussian reflectivity profile. The results show that a resonator of this kind with parameters of practical interest generates a smooth field which fills well the resonator aperture. The field in the far-field zone is concentrated in one peak with a width close to the diffraction limit. The results demonstrate that such a resonator should have a positive influence on the quality of the output radiation also in the case of other gas-flow lasers with a previously established population inversion.

Use of stimulated scattering in improvement of the spatial characteristics of the radiation emitted by a high-power XeCl laser

An experimental study was made of stimulated Brillouin scattering of wide-band depolarized XeCl laser pulses of 300 ns duration in hexane and in quartz rods. The scattered radiation was used to improve the spatial characteristics of the XeCl laser with an output energy of 30 J and an unstable telescopic resonator. This resulted in a threefold increase in the radiation intensity in the focal spot of the laser beam.

Application of unstable telescopic resonators in generation of low-divergence radiation in a pulsed chemical SF6–H2laser with electron-beam initiation

A study was made of the divergence of the radiation generated using unstable telescopic resonators in a pulsed chemical SF6–H2 laser initiated by a transverse electron beam. The duration of laser radiation pulses was ~ 100 ns. Initiation of the active medium resulted in a strong transverse inhomogeneity. It was possible to use telescopic resonators to ensure that the divergence of the output radiation was reduced to ~ 0.15 mrad, which was close to the diffraction limit (~ 0.05 mrad). The laser radiation energy in the far-field zone was then ~ 0.2 J. The energy efficiency in the formation of the radiation was ~ 20%. Comparison with the same laser, but with a plane–plane resonator showed that the axial density was two orders of magnitude higher and the angular divergence was two orders of magnitude lower.

Spatial and temporal characteristics of the radiation from a high-power XeCl laser with an unstable telescopic resonator

The radiation characteristics of an XeCl laser with a 30-liter active medium were investigated as a function of the magnification of an unstable telescopic resonator. Optimal resonator magnifications minimized the divergence at half the radiation energy (M = 18) and ensured the highest radiation brightness in the far-field zone (M = 8.5). When an unstable telescopic resonator was used, the radiation pulses were modulated in the far-field zone and the modulation period was a multiple of the resonator round-trip time for the radiation. The depth of modulation increased with M. The time of formation of the transverse resonator modes increased as their order became lower and decreased with M for the lowest-order modes. The width of each of the lasing lines due to the 0–1 and 0–2 transitions was 25 pm for M = 8.5.

Conditions for cw lasing in a filled open telescopic resonator

The condition ensuring cw lasing is derived and the normal oscillation modes are found for an unstable telescopic resonator filled with an amplifying medium. The diffraction of light at the mirror edges is allowed for. The problem of the normal oscillations is solved for a resonator with cylindrical mirrors. The selected properties of such resonators are considered.

Flashlamp-pumped liquid laser with a diffraction-limited beam divergence of 9 × 10−5rad

An output beam having a divergence 0.5E = 9 × 10−5 rad at half-energy and a total beam energy of 0.7 J was obtained from a laser utilizing a solution of rhodamine 6G in ethanol excited by a flashlamp with a transverse discharge of 250-ns duration. An unstable telescopic resonator in the positive branch with a magnification of 3 was used to achieve this divergence, which corresponded to the diffraction limit at the laser exit aperture.

Design of a CO2gasdynamic laser with selective thermal excitation and an unstable resonator

The task of design of an unstable telescopic resonator for a CO2 gasdynamic laser with selective thermal excitation is considered. The laser is described by parabolized Navier–Stokes equations and by equations of propagation of a field in a resonator in the geometric-optics approximation. A study is made of the dependence of the efficiency on the magnification and distance between the mirrors. It is shown that a high (up to 70%) efficiency of an unstable resonator can be expected for a CO2 gasdynamic mixing laser.

Dye laser with an output energy of 1 J, a beam divergence of 0.3 mrad, and flashlamp excitation

A study was made of the use of an unstable telescopic resonator in a laser utilizing an ethanol solution of rhodamine 6G excited by a coaxial transverse-discharge flashlamp. When the stored electrical energy was 300 J, the output energy of the laser was 1 J and the angle of divergence of the beam at half the maximum energy was 0.3 mrad. A mode structure of the radiation was observed within the limits of this angle and it was found that, in addition with the lowest symmetric modes, modes with a nonzero azimuthal index were generated. The kinetics of thermooptic distortions of the active medium was also investigated.

Single-pulse ruby laser with an unstable telescopic resonator and polarized output

Single-pulse ruby laser with an unstable telescopic resonator and polarized output

High-power system based on a pulse-periodic YAG:Nd3+laser with an unstable telescopic resonator and a two-stage amplifier

A description is given of a high-power YAG:Nd3+ laser system including a master oscillator with an unstable telescopic resonator, polarization coupling-out of radiation, and a two-stage amplifier. The energy, time, spectral, and spatial characteristics of the master oscillator and of the system as a whole were investigated. The system was capable of generating radiation pulses of 10 Hz repetition frequency with a divergence close to the diffraction limit and an output power in excess of 70 MW.

High-efficiency low-divergence pulsed chemical photoinitiated D2–F2laser with an active medium of 6-liter volume

A study was made of the divergence of the radiation obtained from a pulsed chemical photoinitiated D2-F2 laser with active medium of 6-liter volume and efficient utilization of the initiation energy. Selection of an unstable telescopic resonator ensured that the divergence of the laser radiation was close to the diffraction limit and the output energy was ~50–70J. The energy losses (compared with a similar laser with a plane-plane resonator) did not exceed ~30%. The influence of initiation inhomogeneity on the divergence of the output laser radiation was considerably less when an unstable resonator was employed.

Generation of radiation in a resonator under conditions of stimulated Raman scattering in Ba(NO3)2, NaNO3, and CaCO3crystals

A study was made of the generation of Stokes radiation in plane-plane and unstable telescopic resonators under conditions of stimulated Raman scattering in calcite, barium nitrate, and sodium nitrate crystals. The regimes of effective operation of such Raman lasers were determined. It was shown that the efficiency of conversion of the energy of the pump radiation into the energy of the first Stokes component could be increased by ensuring repetitive passage of the pump along a crystal. It was found that the generation of the second Stokes component became weaker under the conditions of pumping of a crystal in an unstable telescopic resonator by a beam opposite to the Stokes radiation leaving the resonator. Measurements were made of the spatial and angular characteristics of the output radiation. In the case of pulsed generation of radiation in a plane-plane resonator it was possible to reduce the angular divergence by the use of a correcting positive (converging) lens.

Asymptotic theory of open unstable telescopic resonators with an active medium

The problem of determining the electromagnetic field in an open unstable telescopic resonator filled with an active medium at high Fresnel numbers in regimes close to the threshold for laser action is considered. The method of matching asymptotic expansions is used to solve the initial equations. The cases when L R 0 ⪡ 1 ( L is the distance between the mirrors and R 0 is the characteristic radius of curvature of the mirrors) and L R 0 ~ 1 are considered. When L R 0 ⪡ 1 , the effect of the edges of the mirrors is analysed analytically. The laser mode of operation is assumed to be the threshold mode. Simplified equations are obtained as a consequence of the asymptotic analysis together with effective boundary conditions on the edges of the mirrors for the amplitudes of the field and the conditions for stationary emission.

Energy characteristics of a ring model of a chemical supersonic DF–CO2laser with an unstable telescopic resonator

A method is proposed for calculating, in the geometric-optics approximation, the energy characteristics of a ring variant of a chemical supersonic DF–CO2 laser with an unstable telescopic resonator formed by mirrors of toroidal shape. Typical distributions of the gain in the active medium are obtained in the absence and presence of lasing, and the intensity of the radiation in the lasing zone is calculated. The chemical efficiency is found as a function of the parameters of the optical system.

Use of unstable resonators in cw chemical lasers with radial flow of a gas mixture

An analysis is made of an unstable telescopic resonator having toroidal mirrors in a ring variant of a cw chemical laser with a radial flow of a gas mixture. A method is proposed for calculating the parameters of such a laser–resonator system in the diffraction approximation using parabolic wave equations. The calculations are made for various values of the magnification in the resonator and the structure of the radiation field is studied in the near- and far-field zones allowing for optical inhomogeneities of the active medium due to the effects of a gasdynamic expansion of the mixture.

Approximate method for calculations of unstable telescopic resonators

A simple method is proposed for the design calculations on unstable telescopic resonators for continuous-flow lasers. The method uses radiation transfer equations in the geometric-optics approximation and is based on averaging all the parameters in the direction of the resonator axis. A CO2 gasdynamic laser is used as an example to demonstrate the high accuracy with which the output power and the intensity at the mirrors are predicted. It is noted that the frequently used isothermal approximation is unsuitable in regimes close to quenching of the laser action.

Calculation of beam divergence of pulsed electron-beam-discharge lasers (EBL)

The beam divergence in electron-beam-discharge lasers is determined by the refraction of the radiation by the gradients of the electron and gas densities. At short pump pulse durations (τ ⪝ 1 μsec) and, accordingly, at high charged-particle densities (ne 1014 cm-3) the divergence is due to the inhomogeneity of the ionization of the active medium. At long durations (τ > 10 μsec) the divergence is determined by the refraction of the radiation by the gas-density gradients produced by the hydrodynamic motion of the active medium during the course of the pump pulse. By using unstable telescopic resonators with dimensions smaller than the energy-input region, it is possible to considerably increase the energy of the radiation whose divergence is due to refraction.

Diffraction effects in a cw HF chemical laser with an unstable telescopic resonator

A self-consistent problem is solved for the radiation field structure of a supersonic cw HF chemical laser with an unstable telescopic resonator (steady-state stimulated emission conditions). The structure of the amplitude and phase diagrams of the laser field in the near and far zones is analyzed for typical conditions, the energy characteristics are calculated, and the angular divergence of the laser radiation is determined for different resonator magnifications. It is shown that using a telescopic resonator in cw HF lasers substantially increases the directionality of the radiation with a moderate decrease in the system efficiency.

Influence of gasdynamic motion of the active medium during a pump pulse on the angular divergence of radiation emitted from electron-beam-controlled lasers

An analysis of the relatjive contributions of refraction and diffraction to the angular divergence of radiation emitted from electron-beam-controlled lasers shows that, in the case of unstable telescopic resonators smaller in size than the energy deposition region, it is possible to increase considerably the energy of that part of the radiation whose divergence is due to diffraction.